A conventional ink jet nozzle for directing ink toward an object to apply inked indicia to the object includes a nozzle plate having an outer surface and a plurality of ink jet openings at the outer surface defined by the ink jet nozzle through which ink is expressed when applying the code or other indicia.
The means for expressing the ink through the ink jet exit openings can vary; however, a relatively commonly employed approach is to employ piezoelectric crystals in operative association with ink feeder tubes leading to the ink jet exit openings. By selectively applying an electrical current to one or more of the piezoelectric crystals, a quantity of ink is expressed or squirted toward an object through selected ink jet exit openings and the desired ink jet pattern is formed.
Ink is expressed through the nozzle on a periodic basis in a system such as that just described and which is known in the art as a "drop on demand" system. Suitable sensing means is normally incorporated in such a system to sense when an object is in position to have a code or other indicia applied thereto.
Over time an inky crust can build up on the nozzle plates of drop on demand ink jet nozzles and the ink jet exit openings can and do become partially or fully clogged or blocked at the nozzle plate. This is aggravated by the fact that ink jet nozzles are often operating under elevated temperatures. Because of this problem, the users of drop on demand systems are often limited as to the types of inks which can be utilized in the nozzles. With prior art ink jet nozzle approaches, an attempt is made to at least slow down the blocking or clogging of the exit openings by employing only relatively light, slow drying inks. In other words, existing approaches can preclude the use of thicker and darker inks which dry faster and shoot further. Thinner, lighter inks are, however, more likely to run or smear on objects to which codes or other indica are applied.
As indicated above, even thinner, lighter inks can cause exit opening obstruction. Consequently, it has been a common practice to occasionally apply liquid solvent to the nozzle plate in the vicinity of the ink jet exit openings manually, typically by wiping the nozzle plate with a cloth impregnated with liquid solvent. This is not satisfactory. First of all, such an approach relies upon an individual to perform the cleaning task responsibly and reliably on a regular basis. In actual practice, however, it is quite common for a worker to put off or delay cleaning until a considerable amount of crusting has already occurred on the nozzle face plate. In any event, the mere action of wiping the nozzle plate with a cloth can actually aggravate the clogging or blocking problem since fibers or dirt from a cloth can enter the very small exit holes.
It is also known in the prior art to periodically spray ink through the ink jet exit openings even when no target object exists in an attempt to keep the ink jet exit openings clear. This strategy is largely unsuccessful in that clogging still occurs. Furthermore, ink is wasted.